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Timeline of Home Computers

Daniel Knight - 2016.01.24

Personal computing never would have gotten started if not for the invention of microprocessors, which puts a computer’s CPU (central processing unit) on a single chip – sometimes with companion chips. Intel released the first commercial CPU in 1971, and the first 8-bit “home computers” arrived just a few years later.

Chips and Kits

The Intel 8008 was the first 8-bit CPU, introduced by Intel in April 1972. The first personal computer based on the 8008 was the SCELBI, which was available assembled or in kit form. With 1 KB of RAM, the kit sold for US$565 and was first advertised in the March 1974 issue of QST, a ham radio magazine.

The 8008’s successor chip, the Intel 8080, was released in April 1974 as an improvement that was also backward compatible with the 8008. This was the CPU used in the MITS Altair 8800, the first really successful personal computer.

This inspired the Zilog Z-80 CPU, which is backward compatible with the 8080 but has an enhanced instruction set, a better interrupt system, and more registers. (The Z-80 was designed by a former member of the Intel team.) Intel would later counter with the 8085. Of the three CPUs, all are supported by CP/M, but the Z-80 had the most success in home computing, perhaps most notably in the TRS-80 sold by Radio Shack.

The competing chip architecture began with the Motorola 6800, which was in many respects comparable to the 8080 and Z-80. All these chips had an 8-bit data bus, a 16-bit address bus to access up to 64 KB of memory, a 16-bit stack pointer, and they even came in the same type of 40-pin package. The 6800 had fast access to the first 256 bytes of memory, addressed I/O devices as memory and thus didn’t need special I/O instructions, and supported direct memory access (DMA), which meant data could be read from a disk directly to memory with no load on the CPU. (The 8080 had more internal registers and did have special I/O instructions.)

The MOS Technology 6502 CPU was developed by former members of the Motorola 6800 team, and it was specifically aimed at potential customers of the 6800 who thought the CPU was too expensive. The goal was a more cost effective CPU, and the 6502 turned out to be that in spades. The 6502 sold for $25 on its release, a far cry from the $175 and up price of competing chips.

This is why Steve Wozniak decided to design the Apple 1 computer (left) around the 6502 CPU. Of course, Motorola responded by cutting the cost of the 6800 to $69, but the 6502 was still the price champion.

Apple, Commodore, Atari, and Acorn would all use the 6502 in their home computers.

One more 8-bit CPU had a role in home computing, the Motorola 6809E. It is best known as the heart of the Radio Shack TRS-80 Color Computer, which first shipped in the second half of 1980. The 6809 was also used in several other personal computers, none nearly as well known as Radio Shack’s CoCo.

Personal computing soon divided into two categories: home computers that had their own operating system and business computers that ran CP/M from Digital Research, a forerunner of MS-DOS. This article skips CP/M machines to focus on the home and education market.

Personal Computer Prehistory

1921: Radio Shack founded to serve amateur radio hobbyists

1928: Motorola begins as Galvin Manufacturing Corporation

1951: Texas Instruments (TI) founded

1954: TI develops the first transistor, designs first transistor radio

September 1980: Commodore VIC-1001 introduced in Japan, essentially a VIC-20 with Japanese Katakana characters instead of PETSCII, causing several potential Japanese competitors to discontinue or postpone their plans to enter the US market.

After 8-Bit Computing

May 1994: Apple introduces first PowerPC Macs, which remain 32-bit until the PowerPC 970 (a.k.a. G5) is introduced in 2002, although even OS X 10.5 Leopard, the last OS version for PowerPC Macs, makes very little use of it 64-bit capabilities

January 2006: Apple begins switch to Intel x86 CPUs with Core Duo models, a chip based on the 32-bit Pentium M design